1. Field of the Invention
The present invention relates to a two-lens-group zoom lens system in which a back focal distance can be short.
2. Description of the Related Art
In a zoom lens system in which a back focal distance can be short (e.g., a zoom lens system for a compact camera), a telephoto type lens system in which a positive lens group and a negative lens group are provided in this order from the object is generally employed because the zoom lens system can dispense with a longer back focal distance unlike a zoom lens system for a single lens reflex (SLR) camera which requires a space for providing a mirror behind the photographing lens. Accordingly, in a SLR camera, a retrofocus type lens system which includes a negative lens group and a positive lens group in this order from the object is generally employed.
In a two-lens-group zoom lens system of the telephoto type, in order to adequately correct aberrations while a compact structure is maintained as well, how to distribute the refractive power (hereinafter, power) over the front and rear lens groups is an important factor. Furthermore, in order to suppress aberration-fluctuations upon zooming, aberrations have to be corrected in each lens group. However, in a zoom lens system in which the half angle-of-view at the short focal length extremity is approximately 35.degree. and the zoom ratio is approximately 2.5, it is difficult to correct aberrations in each lens group. Due to these reasons, i.e., for an attempt to overcome the difficulties on the correcting of aberrations, the number of lens elements has to be increased, the number of cemented sub lens groups has to be increased, and then a three-lens-group zoom lens system has to be employed; and hence, the manufacturing costs increase.